BOOSTER SHOT

Forget seeing double, how about hearing double

There's something about twins that fascinates us— and, of course, we've all heard the stories about twins separated at birth who both marry people named Marvin, wear all-pink clothes, choose the same perfume, select tarantulas as pets and name their pet dogs Fido. (Or something along those lines.)

Some of these amazing "facts" may be myth, others coincidence— "Wow, you both have a golden retriever?"— but a huge number of traits do have genetic influence. Lately off the science assembly line: The ability to hear what the heck someone is saying in one ear when there's music blasting in the other could be largely genetically determined.

The finding, reported in the journal Human Genetics, was reached by scientists at the National Institute on Deafness and Other Communication Disorders after they attended a national twin festival that takes place each year at Twinsburg, Ohio. Capitalizing on the rich concentration of genetically identical pairs attending the jamboree, the scientists administered a battery of "auditory processing" tests to 138 pairs of identical twins and compared the results with the same tests on 56 fraternal twin pairs.

The tests measured how humans deal with conflicting sounds such as different syllables played into left and right ears at the same time.

Since identical twins share 100% of their genes, and fraternal only 50% on average, it's possible to get a measure of how much of a trait is due to genes, and how much to environment, by comparing how closely the results of each fraternal twin pair match each other, compared with each member of identical twin pairs.

The result: In nearly all the tests, identical twin scores were significantly closer to each other than fraternal scores. In one of the tests, 73% of the variation in ability to process sounds was due to genes.

Such auditory processing abilities are important, says the NIDCD's director, Dr. Jim Battey, on a news release from the institute— after all, there's a lot more to hearing than just sound going into an ear. There's also the matter of how well one's gray matter makes sense of it all.

I know. I test well on regular hearing tests but am down in the miserable 5th percentile for hearing in a noisy environment. When talking with people in noisy, high-ceilinged restaurants, I nod, smile, trill with laughter at appropriate-seeming moments and pray that someone didn't just tell me about their Aunt Millie's tragic passing.

(Bill B.: If you wondered what drug I was on when we lunched at Pete's a few months back— I was high on life, no more. I just didn't hear a single thing you said.)